In producing large concrete products such as box sections, round pipes, culverts or manholes, two reinforcement wire mesh cages are required to provide the necessary strength. The cages must be spaced from each other and also spaced from the surfaces of the form used to produce the particular concrete product.
At the present time, the most common spacer used for double cage reinforcement wire mesh for rectangular concrete products, such as box sections, is a spacer that has an eye at each end of a straight section. The eyes serve to space each of the cages from the surfaces of the product form. The straight piece between the eyes determines the spacing between the two reinforcement cages. However, in order to retain these commonly-used spacers in place, the spacers are welded to the mesh at the junction of the eye and straight piece. In some instances, specifications prohibit welding of the spacers to the reinforcement mesh because the welds tend to weaken the tensile strength of the circumferential wire of the mesh. In order to comply with such specifications, the spacers therefore are tied to the mesh by hand using a small soft tie wire. This obviously requires additional labor, thus adding to the cost of the product, and equally important, the soft wires used to tie the spacer to the mesh have little strength and sometimes will break during the production of the concrete products.
There is another form of spacer that is suitable for use on the double cage reinforcement mesh for the large round concrete products. The common spacer used for this purpose is disclosed in U.S. Pat. No. 3,440,792. This spacer has an eye on one end and a J-hook on the other end, the latter being hooked to one cage while the eye is hooked over the circumferential wire of the other cage. The eye serves to space the cage from the form. However, if the wire mesh cages are not precisely made as is often the case, it is possible for the spacer to fall off when the concrete is poured into the forms. This occurs when the spacers are installed loosely on the cages because the cages are too close together and therefore do not exert sufficient force on the spacers to maintain them in place.
Especially with the box section products which use rectangular double cage reinforcement mesh, none of the prior art spacers will hold against forces tending to separate the two cages or tending to move them closer together unless the spacers are welded or tied to the cages. There are also twisting forces which are exerted on the cages while the concrete is being poured into the forms and around the cages, which forces tend to loosen the prior art spacers unless welded or tied onto the cages as is always done for the rectangular cages used in box sections. With the circular cages, welding or tying the spacers to the cages is not generally done, but because of the various forces exerted on the cages during the pipe manufacturing process, loosening of the spacers may still occur.
There is therefore a need for an improved spacer which can be used with the reinforcement cages for rectangular products, such as box sections, which spacers will resist forces exerted on the cages in any direction without becoming loose and falling off the cages during the process of producing the concrete products. There is a further need for a spacer that can be easily installed from outside of the double cage and which does not require welding or other special attachment to the cages, thus speeding up the installation process and making it less costly to the producer of the concrete products.